In particular a stack of folded paper napkins made of elastic fleece material (tissue), with a station for receiving the pressed stack, said station displaying a cover plate disposed parallel to a base plate, at a defined spacing from the latter by means of lateral supports, said cover plate, however, being movable relative to the base plate between a slide-in position and a closing position in a way such that the spacing changes cyclically by a fixed measure during operation.
This embodiment of a machine for enwrapping packaging of relatively elastic stacks of soft paper napkins has been successfully used in practice. From a compressing station, the stack is transferred into the "cassette" of a receiving station, said "cassette" being formed by the base and cover plates, by means of a pusher engaging the stack on one of its narrow sides. In such a transfer, the packaging foil, which is being kept ready, is carried along by the stack into the receiving station. After the receiving operation has been completed, the packaging foil is sealed on the still-open trailing (viewed in the slide-in direction) narrow side of the stack, to form a strip endlessly enclosing the stack (the package is sealed later along the two still-open lateral, narrow sides of the stack).
In order to facilitate the transfer of the stack and the packaging foil into the cassette, it is known also how to slightly increase the spacing between the base and the cover plate during the transfer operation. This spacing is subsequently reduced to the preset defined or nominal spacing once the stack has reached its correct final position in the cassette, so that the packaging foil can finally be sealed in the correct manner.
The size of said "defined spacing", thus the initial or nominal spacing between the base and the cover plate, is of great importance to the reliable and trouble-free operating function of the packaging machine, particularly if the latter is operated at a high rate, i.e. for example when 100 or more stacks are to be processed per minute.
Similar considerations apply to the change in spacing which, in the manner described above, is changed in the course of each operating cycle during at least part of the feeding of the stack into the receiving station. However, while the cyclic change in spacing may always be the same, which means such change can be fixed by relatively simple constructional means, the "defined spacing" between the base and the cover plates generally has to be varied whenever the material of the articles to be packaged changes, that is even with no change in the size and number of paper napkins or the like in the stack, to the extent that even another dye for the material may lead to a change in the height of the stack, to which the nominal spacing (plus the cyclic change in spacing superimposing such nominal spacing at least temporarily) reacts with great sensitivity in the course of transfer. Therefore, in order to avoid too much waste or rejects, said defined spacing has to be carefully readjusted practically with each change of the material of the goods to be packaged, for example with each exchange of the roll of tissue strip.
Heretofore, for such exchange, the packaging machine is stopped, the fastening of the cover plate (cassette) on its individual supports is released and then tightened again after the nominal spacing has been changed as required. This means that the packaging operation, and thus the entire production process, is interrupted for the duration of such an exchange for at least a few minutes, and thereafter has to be restarted again. In addition, the machine operator has to be very skilled, so that any such change in the nominal spacing will, during the subsequent operation, lead to a correct and reliable operation of the receiving station; if not, another readjustment is required.
The object of the invention is to remedy such drawbacks. According to the invention, provision is made so that the defined spacing between the cover and the base plates is variable while the pack-aging contrivance is in operation. In this manner, the receiving station can be adapted almost instantly to any change in the goods being packaged while retaining the measure of the cyclic change in spacing, without temporary shutdown of the machine and hence without noticeable loss in packaging output. Furthermore, during such adaptation, the effect of the latter on the packaging operation can be directly monitored, so that the correct (new) nominal spacing can be found and started all at once.
In the manufacture of packs of folded paper napkins, for example, it is customary in the case of a roll change to insert a roll with a starting material different from the one processed before. There-fore, as a rule, in such an exchange of rolls, the last stack com-prised of the material of the processed roll is directly followed by a stack consisting of the material of the new roll. Also, the stacks comprised of the new material regularly have a different thickness, which means said stacks require a different nominal spacing in the cassette of the receiving station than the stacks packaged previously. Following such an exchange or rolls, the oper-ator of the machine can now react to such exchange solely by adjust-ing the "defined spacing" between the base and cover plates without being required to do anything else. In such an adjustment, there may be a few packs that might have to be rejected as being improperly packaged, depending upon the case or circumstances; how-ever, such loss comes to only a fraction of the loss associated with the aforedescribed procedures based on the prior art. Preferably, the effective length of the cover plate supports is adjustable. Such an adjustment can be made manually, for example with the aid of a crank drive acting on the two supports. However, according to a special embodiment of the invention, provision is made for a tilting bar to be associated with each support; that the supports be connected by a crossbar; and that the bearing of the tilting levers be adjustable with the aid of a cone-and-spindle drive driven by an electric motor. Such an embodiment permits, in a particularly simple manner, superimposition of the cyclic change in spacing between the base and cover plates on the one hand, and changing of the nominal spacing (with any change in the thickness of the stack of goods to be packaged) on the other hand. According to another feature of the invention, provision is made so that the supports are mounted on the one arm of at least one tilting lever, and such that a cam control engages the other arm of said lever. Said cam control assures an always-constant cyclic change in the plate spacing of the receiving cassette in the machine cycle, such change being dependent upon the control cam, whereas the basic or nominal spacing is adjustable by adjusting the bearings of the tilting levers parallel with the longitudinal direction of the supports. If, in a manner known per se, the receiving station is constructed in a displaceable fashion in the slide-in direction in order, on the one hand, to enable insertion of the packaging foil and, on the other hand, to enable driving the receiving cassette close to the compressing station, then further provided is that the supports be supported with the aid of a rotatable block in a rocker arm embodied in the one arm of the tilting lever.